1978 Volume 27 Issue 7 Pages 410-414
Quaternary ammonium salts, amines and alkaloids have sensitively been determined with tetrabromophenolphthalein ethyl ester (TBPE). Accordingly, amines and alkaloids gave strong interferences on the determination of quaternary ammonium salts. Therefore, as a method which supplement this point, a new spectrophotometry has proposed for the determination of quaternary ammonium salts with 2, 6-dichlorophenolindophenol or picric acid, but these have poor sensitivity compared with TBPE. It is found that only TBPE-R3N series show a reversible thermochromism. That is to say, the red colored species, being molecular addition compounds, decreases with the rising of temperature on measurements. On the other hand, blue colored species do not change. The red species contained in blue species disappears at 60°C. It can be assumed the following equation;
TBPE·H·R3N0 warmed _??_ cooled TBPE·H0+R3N0
(Red) (Yellow) (Non)
Therefore, amines and alkaloids give little interferences on the determination of benzalkonium by thermochromism on measurements. The calibration curve was prepared as follows: (15) ml of a standard benzalkonium solution (2.5 × 10-5 M) is taken in the separatory funnel, and 5 ml of borate(0.1 M)-phosphate (0.2 M) buffer (pH 7.5) and 2 ml of TBPE solution (4 × 10-3) are added. It is diluted to 50 ml with water, and shaken with 10 ml of 1, 2-dichloroethane for 5 min. The extracts are centrifuged to remove droplets of water. The absorbance is measured at 610 nm against a reagent blank. ε at 25°C was 7.5 × 104 mol-1 cm-1 and s at 60°C 7.3 × 104 mol-1 cm-1 l.
